PCA Exam- Weeds
What are weeds
plants that interfere with the growing of crops or ornamental plants or cause other types of damage
Invasive weeds
cause ecological damage by displacing native plants and the organisms that feed on them; compete
with ag crops for water and nutrients, causing them to become more susceptible to disease or other
pests
True weeds
adapt well to local climates, soils, and other external conditions
Perennial weeds
capable of reproducing through vegetative structures such as stolons, rhizomes, and tubers; cultural
activities such as hoeing, mowing, or discing can produce new plants; persistent and hard to
eliminate; morning glory
Native weeds
3% plants are weeds; no more than 25-35 weeds in one site
Weeds and their affects
Harbor insects, dry is fire hazard, reduce livestock forage quality and quantity, jeopardize animal and
human health, increase the threat of fire or flooding, interfere with recreational activities, lower land
value, change soil fertility, increase erosion, leaf litter
IDing weeds
recognize differences in flowers, leaves, stems, roots, fruit, seeds, and special structures such as
tubers and rhizomes
Dicots
broadleaves, two seedling leaves (cotyledons), netlike veins, herbaceous or woody plant
Monocots
single grasslike leaf in seedling, veins that run parallel, grasses, sedges, and rushes
Bryophytes
mosses and liverworts; lack a vascular system; occasional pests
Algae
nonflowering aquatic plants that clog storm drains, stream, lakes, ditches and rice fields; carryout
photosynthesis; lack true stems, leaves, and flowers; reproduce through cell division or production of
spores
Best weed stage to kill
, seedling
Winter Annual
germinate in the fall, mature in the winter, die in the early summer, seeds dormant till fall
Summer Annual
germinate in the spring, mature in the summer, die in the fall, seeds dormant till the spring
Annual Weeds
live 1 year or less
Examples of summer annuals
pigweed, puncturevine, barnyardgrass, russian thistle, common purslane, yellow foxtail
Examples of winter annuals
mustard, wild oat, annual bluegrass, burclover, filaree
Biennial weeds
live for two growing seasons; sprout and undergo vegetative growth during the first season, flower,
produce seeds, and die following season
Examples of biennial weeds
bristly oxtongue, poison hemlock, wild carrot, mullien, scotch thistle
Perennial weed examples
curly dock, silverleaf nightshade, field bindweed, alkai sida, dandelion, yellow nutsedge, pacific poison
oak, johnsongrass, bermudagrass
Flowers
contain sexual reproductive organs and differ widely among species; occur singly or compound
inflorescences, groups of flowers arising from main stem
Leaves
arrangement and shape of leaves, vein patterns, and presence of spins or hairs are helpful identifying
characteristics; grasses experts rely on collar region
Stems
weed's basic framework or skeleton; connect roots to other structures providing support for leaves
and flowers as well as channels for transport of nutrients and water
Rhizomes
elongated underground stems that grow horizontally from the plant
Tubers
What are weeds
plants that interfere with the growing of crops or ornamental plants or cause other types of damage
Invasive weeds
cause ecological damage by displacing native plants and the organisms that feed on them; compete
with ag crops for water and nutrients, causing them to become more susceptible to disease or other
pests
True weeds
adapt well to local climates, soils, and other external conditions
Perennial weeds
capable of reproducing through vegetative structures such as stolons, rhizomes, and tubers; cultural
activities such as hoeing, mowing, or discing can produce new plants; persistent and hard to
eliminate; morning glory
Native weeds
3% plants are weeds; no more than 25-35 weeds in one site
Weeds and their affects
Harbor insects, dry is fire hazard, reduce livestock forage quality and quantity, jeopardize animal and
human health, increase the threat of fire or flooding, interfere with recreational activities, lower land
value, change soil fertility, increase erosion, leaf litter
IDing weeds
recognize differences in flowers, leaves, stems, roots, fruit, seeds, and special structures such as
tubers and rhizomes
Dicots
broadleaves, two seedling leaves (cotyledons), netlike veins, herbaceous or woody plant
Monocots
single grasslike leaf in seedling, veins that run parallel, grasses, sedges, and rushes
Bryophytes
mosses and liverworts; lack a vascular system; occasional pests
Algae
nonflowering aquatic plants that clog storm drains, stream, lakes, ditches and rice fields; carryout
photosynthesis; lack true stems, leaves, and flowers; reproduce through cell division or production of
spores
Best weed stage to kill
, seedling
Winter Annual
germinate in the fall, mature in the winter, die in the early summer, seeds dormant till fall
Summer Annual
germinate in the spring, mature in the summer, die in the fall, seeds dormant till the spring
Annual Weeds
live 1 year or less
Examples of summer annuals
pigweed, puncturevine, barnyardgrass, russian thistle, common purslane, yellow foxtail
Examples of winter annuals
mustard, wild oat, annual bluegrass, burclover, filaree
Biennial weeds
live for two growing seasons; sprout and undergo vegetative growth during the first season, flower,
produce seeds, and die following season
Examples of biennial weeds
bristly oxtongue, poison hemlock, wild carrot, mullien, scotch thistle
Perennial weed examples
curly dock, silverleaf nightshade, field bindweed, alkai sida, dandelion, yellow nutsedge, pacific poison
oak, johnsongrass, bermudagrass
Flowers
contain sexual reproductive organs and differ widely among species; occur singly or compound
inflorescences, groups of flowers arising from main stem
Leaves
arrangement and shape of leaves, vein patterns, and presence of spins or hairs are helpful identifying
characteristics; grasses experts rely on collar region
Stems
weed's basic framework or skeleton; connect roots to other structures providing support for leaves
and flowers as well as channels for transport of nutrients and water
Rhizomes
elongated underground stems that grow horizontally from the plant
Tubers
